Eutectic beams are commonly used to refrigerate the cargo spaces of delivery trucks. A eutectic beam works on the principal of heat transfer during freezing and melting of a eutectic solution, such as sodium nitrate (NaNO.sub.3), ammonium chloride (NH.sub.4 Cl), brine, and the like. The specific eutectic solution used is determined by the desired temperature of the cargo space. A eutectic beam may be charged during night storage of an associated truck, for example, by connecting the eutectic beam to an external condensing unit via flexible hoses; or, by operating a refrigeration system on the truck from a commercial power supply. If the truck has a refrigeration system, a eutectic beam may also be charged while the truck is in use.
A eutectic beam comprises a housing, a eutectic solution in the housing, and a metallic cooling pipe in the eutectic solution. When the eutectic solution is to be frozen, a refrigeration system, ie., a condensing unit, is connected to the metallic cooling pipe, and a refrigerant is passed through the metallic pipe. The metallic pipe functions as an evaporator, removing heat from the eutectic solution until it is frozen. For purposes of simplicity, the metallic pipe in a eutectic beam will be hereinafter called the evaporator tube.
Eutectic beams commonly utilize plastic for the housing, such as polyethylene, with the metallic evaporator tube being constructed either of copper, or steel tubing coated with a 1 mm thick protective layer of polyethylene. Plastic is commonly used for the housing, instead of metal, because of corrosion problems.
The plastic housing of eutectic beams of which I am aware has a generally rectangular housing having side walls and end walls, and the evaporator tube has a generally U-shaped configuration which includes a curved bight and first and second leg portions. The ends of the leg portions extend in liquid-tight relation through one end wall, and the bight is supported by the opposite end wall by a sliding clamp mounting arrangement which allows for differences in thermal expansion. The housing is usually formed by rotational molding or rotational casting, with two unions at the ends of the leg portions being mounted in one end wall of the mold and the mounting arrangement for supporting the bight being mounted in the other end wall of the mold, prior to introduction of the plastic in the mold. The mold is then chilled and the housing with the evaporator tube is stripped from the mold.
The evaporator tube is quite long, measured from the end wall which supports the two leg portions to the support at the midpoint of the bight. Thus, as the eutectic turns to liquid during usage in a truck, the evaporator tube flexes as the truck encounters bumps and seams in the road, with this constant flexing leading to fatigue cracks in the metal evaporator tube. Fatigue cracks allow refrigerant to escape when the evaporator tube is connected to a refrigeration system. Thus, it would be desirable, and it is an object of the invention, to provide a new and improved eutectic beam which significantly reduces the development of fatigue cracks during usage of the eutectic beam.